1. Field of the Invention
Remote sensing data form the basis for many different types of studies of the environment around us, ranging from the discovery of valuable mineral deposits, for example, by satellite-supported mapping of the earth to the acquisition of environmentally relevant data. Thus a large circle of users can put these data effectively to use. The same data can be used to solve problems in various areas of interest.
2. Description of the Related Art
A first aspect of the invention relates to a method and arrangement/apparatus for processing remote sensing data, especially remote sensing data which have been recorded by a satellite.
Existing methods and systems for the automatic processing of remote sensing data usually serve a single purpose. In some cases, it is assumed that the user has a great deal of knowledge about satellites, about remote sensing data, and about how to process such data. The networking of the reception, storage, and distribution of the remote sensing data and of the data products derived from them will continue to increase both nationally and internationally in the coming years. Thus larger quantities of remote sensing data, which can be used to solve a wide variety of problems, will become available. Aside from that, the databases already in existence are not being utilized as fully as possible. New remote sensing missions, furthermore, are being launched at regular intervals, which means that the quantities of data can be expected to continue to increase. For this reason, it is becoming more difficult for the user of the remote sensing data and of the data products to retain an overview of the existing possibilities and to select the right data and the right products.
It is an object of the first aspect of the present invention to provide a method and arrangement for processing remote sensing data, which make it possible to minimize the effort required of the user of the remote sensing data, despite the existence of a large number of different goals which can be achieved by the use of such data. In particular, the object is to make it unnecessary for the user to have wide-ranging expert knowledge about satellites and/or the acquisition of remote sensing data.
A second aspect of the invention relates to a method and arrangement/apparatus for the selection of remote sensing data, especially remote sensing data which have been recorded by a satellite.
In the existing systems for searching available remote sensing data to find those which are suitable for a specific purpose, it is currently assumed that the user has a great deal of knowledge about satellites and about remote sensing data. As the variety of data increases, there will necessarily be a corresponding increase in the number of selection criteria.
The networking of the reception, storage, and distribution of the remote sensing data and of the data products derived from them will continue to increase both nationally and internationally in the coming years. Thus larger quantities of remote sensing data, which can be used to solve a wide variety of problems, will become available. Aside from that, the databases already in existence are not being utilized as fully as possible. New remote sensing missions, furthermore, are being launched at regular intervals, which means that the quantities of data can be expected to continue to increase. For this reason, it is becoming more difficult for the user of the remote sensing data and of the data products to retain an overview of the existing possibilities and to select the right data and the right products.
It is an object of the second aspect of the present invention to provide a method and arrangement for selecting remote sensing data, which make it possible to select from among a large number of available alternatives those which come closest to meeting the user's requirements. It should be possible to obtain reproducible results in this way, and there should be no need for expert knowledge.
A third aspect of the invention relates to a method and arrangement/apparatus for the automatic georeferencing of remote sensing data, especially of remote sensing data which have been recorded by a satellite.
The georeferencing of the remote sensing data (i.e., the correlation of the remote sensing data to geographic information, e.g., from a map of the earth's surface) is a fundamental task of the further processing of the remote sensing data. It is a prerequisite in particular for the generation of derived data, such as data which can be useful to agriculture. Because the remote sensing data of satellites are present initially in the form of so-called satellite projections, and because these are usually distorted in comparison with geographic projections, we also speak of the “rectification” of remote sensing data or of satellite images. There are essentially two different procedures which have been used in the past to do this. In the method of position calculation, a projection model is used, which simulates the motion of the satellite as accurately as possible. For this purpose, it is necessary to have data on the satellite's orbit, on the position of the satellite at the time in question, on the position of the recording system (including one or more sensors) in the satellite, on the projection lenses, and on the form of the space body.
In the method based on so-called “control points”, characteristic image structures are used, which can be identified in both the satellite image and again in the reference image. Positions can thus be determined by comparing the positions in the two images. In contrast to the projection model, however, only the positions of the control points are known. All other positions are determined or assigned by the use of an interpolation model. Combinations of the two methods are also used.
In both of these cases, the goal of the georeferencing is to correlate the measured pixels of the remote sensing data with geographic data. In the case of interactive methods (i.e., methods requiring the participation of a human operator), a geographic reference (e.g., a rectified image or a geographic map) is usually used to achieve this geographic correlation. The automatic methods are based in most cases on the exact knowledge of the projection geometry and on the availability of the corresponding projection parameters required.
A satellite projection is a projection obtained by projecting an observed object (e.g., an area of the earth's surface or an area of some other body in space, e.g., another planet) onto the sensor plane (or image plane) of the satellite. The result of the projection thus depends on the position of the satellite and on the angle at which the satellite is viewing the object being observed for remote sensing. The remote sensing data present in the satellite projection may already have been subjected to certain corrections (e.g., correction of the offset, amplification of a sensor signal) and/or to other operations. In particular, the measurement signals supplied by a sensor of the satellite during a scanning process may already have been converted into the common coordinate system of the satellite projection. For example, the sensor's measurement signals which are used are obtained successively during the scanning process.
In many methods of georeferencing, the information content of the remote sensing data (e.g., multi-spectral data) is altered. For example, the data can be rectified onto a fixed data grid (e.g., a grid of lines of equal geographic latitude and longitude), and each of the individual pixels mapped onto this grid will usually represent a combination of several pixels, which were originally adjacent to each other in the satellite projection. What takes place, therefore, is a kind of averaging. As a result, the grayscale values measured by a sensor of the satellite, for example, or the spectral characteristics measured by the satellite are not preserved and are therefore unavailable for further processing only in their original form. This procedure, however, has become established especially in the area of interactive image processing, because the operator can compensate intuitively for possible changes during the further course of processing.
The change in grayscale values or spectral characteristics, however, is troublesome precisely in cases where the data are to be subjected to further processing automatically and physical relationships are to be taken into account. After the averaging, the original grayscale values or the original spectral characteristics can no longer be calculated. The results will therefore suffer from a certain error. The goal, however, is to derive highly accurate quantitative data and/or parameters.
One of the objects of the present invention is therefore to provide a method and arrangement of the type indicated above in which physical properties such as the grayscale values and spectral characteristics of the remote sensing data measured by the satellite remain preserved. In addition, there should be no need for the operators to make any interventions or to take any actions, and there should be no need for the user to have expert knowledge to complete the georeferencing successfully.